Ryan Compton

Phase matching in femtosecond BOXCARS

We analytically describe the effect of phase-matching conditions on femtosecond BOXCARS line shape and demonstrate quantitative agreement with experimental spectra for the oxygen vibrational transition, DG01=1556.4 cm(-1).

Observation of coherent oscillations in plasma-enhanced atomic layer deposition Ag films

Acoustic oscillations were observed in ultrafast transient absorption of nanostructured Ag films produced by plasma-enhanced atomic layer deposition (PEALD). The oscillations are attributed to modulations of localized surface plasmon resonance (SPR) bands that naturally arise in the PEALD films and can be described as two lateral modes (∼50 and 100 GHz) with different dephasing times. Contributions from electron-phonon coupling and lattice dynamics in the transient response vary systematically with the probe wavelength relative to the SPR maximum (500–1000 nm).

Tunable broadband optical generation via giant Rabi shifting in micro-plasmas

Broadband, coherent radiation in the optical frequency range is generated using micro-plasma channels in atmospheric gases in a pump-probe experiment. A micro-plasma medium is created in a gas by a focused intense femtosecond pump pulse. A picosecond probe pulse then interacts with this micro-plasma channel, producing broad, coherent sidebands that are associated with luminescence lines and are red- and blue-shifted with respect to the laser carrier frequency. These sidebands originate from the induced Rabi oscillations between pairs of excited states that are coupled by the probe pulse. These excited states become populated in the process of plasma cooling. Thus, the sideband radiation intensity tracks the micro-plasma evolution. The sidebands incorporate Rabi shifts corresponding to varying value of the electric field magnitude in the probe pulse: this makes them broad and malleable to tuning. The intensity of the probe beam ~ 1010 W cm-2, creates a maximum sideband shift of > 90 meV from the carrier frequency, resulting in an effective bandwidth of 200 meV. The sidebands may be effectively controlled by the intensity and temporal profile of the probe pulse. The giant Rabi shift is both tunable and coherent over a wide range of frequencies and over a wide range of atomic transitions. The fact that the coherence is observed in a micro plasma demonstrates that Rabi cycling is possible at high temperature with moderately high laser intensities (1010 W cm-2) as long as transitions close to the driving frequency (▵ ~ 2% ωc) are available.

Strong Field, Ultrafast Ionization of Atoms and Molecules in the Mid-Infrared

The ionization yields for atomic and molecular targets in the strong field, mid-IR regime reveal an exponentially increasing ionization probability as the excitation wavelength increases. The counter-intuitive trend is attributed to transient Rydberg ionization.